1. Field of the Invention
The present invention relates generally to corneal contact lenses and their use in treating myopia. More particularly, the present invention is directed to corneal contact lenses which are shaped to provide gradual altering of the patient's cornea during continued wear to reshape the cornea to reduce the myopic condition.
2. Description of Related Art
Myopia, also known as nearsightedness, is a condition where the radius of curvature of the cornea is smaller than normal. Individuals with this condition have difficulty in focusing on distant objects because the cornea the curved too sharply to provide adequate focusing. Myopia is a common condition for which no entirely suitable permanent treatment has been developed.
One approach to correcting myopia is through surgical reshaping of the cornea. However, such surgical procedures have not been entirely proven and there is some question as to the permanency of the surgically altered lens shape.
Another approach is to alter the corneal shape by wearing corneal contact lenses which are designed to continually exert pressure on selected locations of the cornea to gradually force or mold the cornea into the desired normal corneal curvature. A retainer lens is then worn on a part time basis to prevent the cornea from returning to its original shape. This method of treatment is commonly referred to as orthokeratology. The success of any treatment by orthokeratology is dependent upon the shape and structure of the corneal contact lens.
My prior U.S. Pat. No. 4,952,045 discloses a contact lens which is specifically designed for use in treating myopia. The lens includes a central zone, a tear zone located concentrically around the central zone and an outer peripheral zone which is located concentrically around the tear zone. This lens is designed specifically so that the radius of curvature of the tear zone is smaller than the radius of curvature for both the central zone and peripheral zone. I discovered that this corneal lens configuration is useful in changing the shape of the myopic cornea to that of a normally shaped cornea. In addition, the sharper curve of the tear zone provides a ring-shaped area where tear fluid is concentrated between the lens and cornea.
Although the corneal contact lens disclosed in U.S. Pat. No. 4,952,045 is well-suited for its intended purpose, there is continual need for improvement of the design of such a lens to make it better suited for use in treating myopia. For example, in many situations myopic patients require a multiple focus lens, such as a bifocal lens, to provide adequate near and far vision. It would be desirable to provide such people with a multiple focus lens which also includes the features of my prior lens.